Kiln heating control system

ABSTRACT

A control system for an electrically heated ceramic kiln utilizes a plurality of heating coils and a plurality of switching elements connected to the coils so that each coil has more than one heating level. Timing means provide output time signals at predetermined intervals to a logic circuit, with the logic circuit effecting operation of predetermined sequences of switching elements to control the heating coils.

United States Patent 1191 Flasza et al.

1111 3, 55,452 Dec. 17, 1974 KILN HEATING CONTROL SYSTEM 3,489,913 1/1970 Wildi 219 485 3,560,712 2/1971 Toohill 1 219/483 [76] Inventors-l Mlchaelll Flam 3302 59th 3,818,183 6/1974 Masson 219/501 x Ave., Clcero, Ill. 60650; Leonard gi r gzi g Primary ExaminerJ. D. Miller g Assistant ExaminerFred E. Bell [22] Filed: Nov. 29, 1973 [2!] Appl. No: 420,151 [57] ABSTRACT v A control 'system for an electrically heated ceramic 52 U Cl 2 9 2 9 .2 kiln utilizes a plurality of heating coils and a plurality [51] Int. Cl. Hb 1/02 of Switching elements Connected to the Coils 50 that [58] Field ofSearch... 219/483-487, each Coil has more than one heating level- Timing 219 492 50 means provide output time signals at predetermined intervals to a logic circuit, with the logic circuit effect- 5 References Cited ing operation of predetermined sequences of switching UNITED STATES PATENTS elements to control the heating coils. 3.453.415 7/l969 Hermes et al 219/486 7 Claims, 3 Drawing Figures flVf/V #ilf/l/' [0/15 64 my: /6

[I I 70mm? an! 11 I [X7 7 106/6 397m 4 g 7 a"/// 44 95 m1 5mm 72M 5, 3',

96 [Mom/4 7 mm Q I r. Z u A 705 18 I 7 f 3 29/?! now 3 v 2; "[A 3 lair 7 4 m V k m i6 p v 32 Mfl a: l l 5 f flown away I r l/ +51! v /Z KILN HEATING CONTROL SYSTEM SUMMARY OF THE'INVENTION The present invention relates to a control system for use in ceramic kilns and has particular relation to means providing automatic heat control for such a kiln.

A primary purpose of the invention is a simply constructed reliably operable automatic control system for the heating coils of reliably operable automatic control system for the heating coils of a ceramic kiln.

Another purpose is a control system of the type described utilizing independent switching elements for each heating level of each coil.

Another purpose is a control system of the type described utilizing solid state timing means for providing timed output signals at predetermined intervals.

Another purpose is a control system of the type described using a simply constructed logic block, con trolled by a routine switch and time signal, to effect operation of the switching elements.

Another purpose is a ceramic kiln heating control system having alogic output for each switching element, with each switching element controlling one level of heat for one'coil. Other purposes will appear in the ensuing specification, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS and time encoding system, and I i l coil 16, a top coil 18 and a bottom coil 20. Such a coil arrangement is conventionalin kilns of the type described. A timer'and time encoding block is indicated at 22 and is connected by output lines 24, 26, 28 and Y 30 to a logic block 32. The logic block has a series of output lines designated respectively as Cone, B-Low, B-Med., B-I-li, with the latter three representing the low, medium and high heats for the bottom coil. T- Low, T-Med. and T-Hi represent the low low, medium and high heats for the top coil and E-Low and E-Hi represent the low and high heats for the external coil. There is also a lid vent output which may not be necessary in every application. These respective output lines are designated by the numbers 34 through 52, respectively.

A 240/volt power supply is indicated generally at 54 and includes hot terminals 56 and 58 and a ground ter- FIGS is a schematic of the relay switching and inter- I face portion of the control system of FIG. 1.

- DESCRIPTION OF THE PREFERRED EMBODIMENT "It has been the practice in the operation of ceramic kilns, particularly those suitable for hobby use, to have the kiln operator set aseries of switches to determine which heatingcoils are in operation at a particular time. Normally,since the operation of the heating coils durin'g'a complete kiln cycle must'change, the operator periodically returns to the kiln to reset the heat control switches. Or the operator must constantly stay at the kiln to make sure that the switches are set at appropriate times. The present invention provides a control system for kiln heating coils of the type described which,

is totally automatic. A timing circuit provides output triggering pulses at predetermined intervals, for example every half hour, to a counter, which in turn provides binary inputs to a logic'block, with the timed inputs to the logic block providing different combinations of output signals to effect the operation of the switching elements for the heating coils. The sequence of the switching elements operation may be changed depending upon the particular routine that the kiln operator is following. Thus, there are additional inputs to the logic block, depending upon the particular routine being followed by the kiln operator.

In FIG. 1, a kiln power supply is indicated at 10 and a relay switching and interface block is indicated at 12. The oven or kiln heating coils are indicated as being positioned within the block 14 and include an external minal 60.

The power supply 10 is connected to the ground and hot terminals 60 and 58 through a selector switch designated generally at 62.

vAbuz zer or similar alarm indicated at 64 is connected on one side to an SCR 66 and through'associated control circuitry to the cone output34 of the logic block 32. The opposite side of alarm 64 is connected to power switch 62. e

Details of the timer and time encoding circuit are illustrated in FIG. '2. A unijunction transistor 68 has one base 70 connected through a resistor 72 to ground bus 92 and a second base 74 connected through a resistor 76 to a +5 volt bus 78.'The emitter 80 of transistor .68 is connected between a grounded capacitor 82 and the combination of a fixed resistor '84 and a variable resistance 86, the upper end of which is connected to the +5 volt bus 78. The emitter 80 is also connected to a transistor 88, whose base is connected by a capacitor to ground bus 92 and by a resistor 94 to cone output 34. As shown in FIG. 1, cone output 34 is also connected through a resistor 96, capacitor 98 and resistor 100 to the gate of SCR 66 for purposes described hereinafter.

Base 70 of unijunction transistor68 is connected to adivide-b'y -l2 counting circuit 102 which may be an SN 7492. Counting circuit 102 in turn is connected to a second divide-by-IZ counting circuit 104, also an SN 7492. If the unijunction transistor 68 provides an output pulse every 12.5 seconds, counting circuit 104 will provide a square wave output every 30 minutes. The

- output from counting circuit 104 provides the input for a four-bit binary counter 106, for example an SN7493. The output of binary counter 106 will be a four-bit binary number representative of the elapsed time the unit has been in operation. The four output lines from binary counter 106 are indicated in FIG. 1 by the numerals 24-30 and are designated as inputs T through T for the logic block 32.

The timer and time encoding block 22 also includes a routine switch indicated generally at 108 having one input 110 connected to the +5 volt bus 78 and a second input 112' connected to the ground bus 92. The switch 108 may be used by the kiln operator to select a particular heating cycle and is shown in the number I position. As can be easily seen, there are arrangements for two additional positions or routines. The output contacts 114 and 116 of the routine switch provide the T and T inputs to the logic block 32. Thus, the particular routine, as well as the elapsed time, will provide six logical inputs to the logic block 32. The logic outputs will be present on output lines 34-52.

FIG. 3 shows the relay switching and interface circuit. Each of the logic outputs on lines 36 through 50 Thus, closure of a high relay connects the top and bottom sides of its heating coil between the two hot terminals of the 240 volt power supply to provide high heat for that particular coil.

will be connected to the top side of one of resistors 118- 5 When B-Med. relay coil is closed, ground bus 146 The bottom side of each resistor 118 is connected to will be connected via line 148 to the center tap of the gate 120 of an SCR 122. The cathode of each of the botom coil 20, with the result that the bottom half of SCRs'is connected to ground bus 124, with h of the that coil will be connected between ground and hot teranodes of the SCRs being connected to the parallel minal to Provide a 120 heating PPl to the bi i f an i di l 126 and a relay il coil. in like manner, when T-Med. relay coil 1s closed, 128. The top of the indicators and relay coils are conground bus 146 l be connecied 150 to the nected to a power bus 130, which in turn is connected centerfap of P coll 18 to P med'um heat at the to the power switch 62. Thus, when any one of the logi- IQPPW cal outputs 36-50 has a positive voltage thereon, this When B-Low relay coil is closed, ground bus 146 will voltage will cause a particular SCR to conduct, closing be connected via line 139 to the top side of bottom coil the relay associated therewith, to complete the power 20 to provide low heat. When connected in this manner connection for a particular heating coil. bottom coil 20 will have its total coil distance con- Logical output 52, or the lid vent output, is connected between ground and hot terminal 58, whereas, nected to a resistor 132 in turn connected to the gate 2 in the diu Position. nly half of 20 will be of an SCR 134, with the cathode of SCR 134 being con- 0 nected between ground and hot terminal 58. In like nected to the ground bus 124 and the anode being conmanner, when the T-Low relay coil is closed, ground nected directly to a lid vent solenoid 136. Thus, a posibus 146 will be connected through line 150 to the top tive voltage at output 52 from the logic block 32 will side of heating coil 18 to provide low heat for the top cause operation of the lid vent solenoid 136. This par- Coll- I ticular feature is not necessary in every application of Returning to the overall operation of the system, in the kiln control system. a hobby kiln of the type described, there may be several Turning to the high voltage supply 54, hot terminal different routines, depending upon the type of materi- 56 is connected by line 138 to the B-Hi relay coil als being used. In this particular case provision is made contacts, the T-Hi relay coil contacts, and the E-Hi for three. The inputs to the logic block 32 are derived relay coil contacts. The closure of the B-Hi relay coil from elapsed time and the particular chosen routine contacts will thus place the voltage from terminal 56 of and are placed on inputs T through T These inputs the 240 volt supply on line 139 which is connected to may be either a logical 0 or a logical l. The outputs the top side of bottom coil 20. The bottom side of botfrom logic block 32 will either be a logical O or a logical tom coil 20 is connected by line 140 to hot terminal 58. 35 1, i.e., a positive voltage, depending upon the routine In like manner, closure of the T-Hi relay will place the chosen and the time. Set out below is'a table showing voltage from terminal 56 on line 142 which is conthe relationship between the routine, the inputs and the nected to the top side of top coil 18, with the bottom outputs. Although we have not shown the particular side of coil 18 being connected to terminal 58 through logic circuit, the assembly of such a circuit is well line 140. Closure of the E-Hi relay coil will place the 40 within the skill of the art and would normally be imple' voltage. from terminal 56 on line 144 which is conmented by Texas Instruments, Inc. SN 7400 series logic nected to thitop idgoi e rternal coil l 6, the bottom integrated circuits, or by a combination of NAND gates .side of which is g onnected to terminal 58 by bus 140. and hex inverters.

INPUT OUTPUT sT1 n 2 1 o) H L iI M L II M L 000000 000010011 000001 000010011 ROUTINE No.1 000010 010010101 000011 010100101 000100 010101000 000101 101001000 1010000 000010011 010001 000010011 010010 000010101 010011 010010101 ROUTINE NO. 2 i 010100 010100100 010101 010100100 010110 010101000 010111 010101000 011000 101001000 '110000 000010011 110001 000010011 110010 000010011 110011 000010011 110100 000010011 ROUTINE No.3 110101 000010011 {110110 010010100 110111 010010100 111000 010100100 111001 010100100 111010 010101000 111011 010101000 t1111 00 101001000 As an example, if Routine 1 has been chosen, the inputs from T and T, are both logical zeros, and at the beginning of the time cycle all other inputs are logical zeros. The output for such a sequence would be a logical one on T-Low and a logical one on B-Low and Lid. Thus, the top and bottom coils will be at their low heat and the lid relay would be operated to indicate that the lid is being vented. At each subsequent half hour, the outputs may change. At the end of the'first half hour, for Routine Number 1, the outputs are the same. However, at the end of thefirst hour, E-Low has a logical one providing low heat on the external coil, there is low heat on the top coil, and medium heat on the bottom coil. A half hour later there is still low heat on the external coil, medium heat on'the top coil and medium heat on the bottom coil. A half hour later there is still low heat on the external coil, medium heat on the top coil'and high heat on the bottom, and the lid has closed. Beginning the final half hour, there is high heat on the external coil, high heat on the top coil, and high heat on the bottom coil. Other routines would operate in a similar manner as shown in the above table.

When the routine has been completed, there will be an output of logical l on the cone output. This output is effective to stop the timing circuit, by disabling the operation of transistor 88, permitting SCR 66 to fire, causing the buzzer to operate, indicating to the operator that the kiln cycle has been completed.

Although the invention has been described in connection with particular types of switching devices, i.e., SCRs, obviously the invention should not be so limited. Nor should the invention be limited to a particular type of logical array for the logic block. What is important is to provide for predetermined outputs based on certain input sequences.

Whereas the preferred form of the invention has been shown and described herein, it should be realized that there may be many modifications, substitutions and alterations thereto.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A control system for an electrically heated ceramic kiln including a plurality of heating coils, a plurality of i switching elements connected to said coils, there being at least two switching elements for each coil to provide at least two heating levels for each coil,

timing means for providing periodic controlled output time signals, and logic means connected to said timing means and to said switching elements, with sequential time signals providing predetermined outputs from said logic means to cause the operation of predetermined switching elements.

2. The control system of claim 1 further characterized in that there are three heating coils, an external coil, a top coil and a bottom coil, there being three switching elements for the top and bottom coils and two switching elements for the external coil.

3. The control system of claim 1 further characterized by and including a routine selector switch connected to said logic means, with the inputs to said logic means from said routine selector switch cooperating with said output time signals to determine the predetermined outputs from said logic means.

4. The control system of claim 1 further characterized in that each of said switching elements include a relay coil and a semiconductor switching element.

5. The control system of claim 1 further characterized in that said timing means includes a plurality of solid state divide circuits, with the output of said timing means being 30-minute separated triggering signals.

6. The control system of claim 5 further characterized in that said timing means includes a unijunction transistor.

7. The control system of claim 1 further characterized that at least one of said coils has top, bottom and center taps, with one of said top and bottom taps being directly connected to a hot voltage terminal, there being three switching elements for said coil, closure of one switching element connecting the center tap to ground, closure of a second switching element closing the other of said top and bottom tap to ground and closure of the third switching element connecting the other of said top and bottom tap to a hot voltage terminal. 

1. A control system for an electrically heated ceramic kiln including a plurality of heating coils, a plurality of switching elements connected to said coils, there being at least two switching elements for each coil to provide at least two heating levels for each coil, timing means for providing periodic controlled output time signals, and logic means connected to said timing means and to said switching elements, with sequential time signals providing predetermined outputs from said logic means to cause the operation of predetermined switching elements.
 2. The control system of claim 1 further characteriZed in that there are three heating coils, an external coil, a top coil and a bottom coil, there being three switching elements for the top and bottom coils and two switching elements for the external coil.
 3. The control system of claim 1 further characterized by and including a routine selector switch connected to said logic means, with the inputs to said logic means from said routine selector switch cooperating with said output time signals to determine the predetermined outputs from said logic means.
 4. The control system of claim 1 further characterized in that each of said switching elements include a relay coil and a semiconductor switching element.
 5. The control system of claim 1 further characterized in that said timing means includes a plurality of solid state divide circuits, with the output of said timing means being 30-minute separated triggering signals.
 6. The control system of claim 5 further characterized in that said timing means includes a unijunction transistor.
 7. The control system of claim 1 further characterized that at least one of said coils has top, bottom and center taps, with one of said top and bottom taps being directly connected to a hot voltage terminal, there being three switching elements for said coil, closure of one switching element connecting the center tap to ground, closure of a second switching element closing the other of said top and bottom tap to ground and closure of the third switching element connecting the other of said top and bottom tap to a hot voltage terminal. 